/Engine/Plugins/Runtime/MassEntity/Source/MassEntity/Public/MassProcessor.h
Adds SubProcessor to an appropriately named group. If RequestedGroupName == None then SubProcessor will be added directly to ChildPipeline. If not then the indicated group will be searched for in ChildPipeline and if it's missing it will be created and AddGroupedProcessor will be called recursively
void AddGroupedProcessor ( [FName](API\Runtime\Core\UObject\FName) RequestedGroupName, [UMassProcessor](API\Plugins\MassEntity\UMassProcessor) & SubProcessor )